Cyclic polymerization

ABSTRACT

A method for cyclic polymerization, wherein a fluorine-containing monomer is subjected to cyclic polymerization, the fluorine-containing monomer having two carbon-carbon multiple bonds, each having different polymerizability, as linked by a linking chain having a straight chain portion to from 2 to 7 atoms, and having a fluorine content of at least 10% by weight.

This invention relates to a method for cyclic polymerization, and moreparticularly, it is concerned with a novel cyclic polymerization toproduce a fluorine-containing polymer having a cyclic structure in itsmain chain by use of a particular fluorine-containing monomer.

With regard to the cyclic polymerization of hydrocarbon-type monomers,there have been done various researches, and a multitude of reports havebeen known in general, inclusive of three-membered cyclic polyether tolarge-membered cyclic polyether.

On the other hand, there have been known various fluorine-containingpolymers, of which polytetrafluoroethylene and many others are alreadypractically put into industrial use. However, these fluorine-containingpolymers mostly contain therein the straight main chain based on vinylmonomer such as fluoro-olefin, (meth)acrylate having the fluoro-alkylgroup in its side chain, etc. There has also been known a high molecularweight compound such as perfluoro-polyether to be obtained by thering-opening polymerization of a hexafluoropropylene oxide. In thiscase, too, the structure of the main chain is of the straight chain.Furthermore, in recent years, attempt has been made on the synthesis ofa polymer having a cyclic structure of ##STR1## in the main chain by themetathesis polymerization of a monomer such as ##STR2## in the presenceof a molybdenum type catalyst (vide: A. Alimuniar et al., Polymer, 198627 1281.). These fluorine-containing polymers are obtained by theordinary vinyl polymerization, or the ring-opening, or the ring-openingmetathesis polymerization, and not by introduction of the cyclicstructure into the main chain due to the cyclic polymerization fromstructure straight chain monomers.

It has only been known that a compound of a general formula: CF₂═CF--(CF₂)_(x) CF═CF₂ (where: x is an integer of from 1 to 5) undergoesthe cyclic polymerization by the gamma rays (vide: L. A. Waal,Fluoropolymer, Wiley-Science, 4, High Pressure Polymerization, p 127).It has also been known that a compound represented by the followinggeneral formula: CF₂ ═CF--CF₂ --CFCl--CF₂ --CF═CF₂ is polymerized toyield a transparent and highly elastic film which is excellent in itsheat-resistance and oxidation-resistance (vide: D. S. Ballentine et al.,U.S. Atomic Energy Commission, BNL-294 (T-50) 18, 1954). All thesemethods are, however, the high pressure polymerization method whichrequire a pressure value as high as 10,000 atm. or above, hence themethod possesses a disadvantage such that it is difficult to be put intoindustrial exploitation.

Moreover, in British patent specification No. 1,106,344, U.S. Pat. No.3,418,302, and others, there is described a method of cyclicpolymerization of a monomeric substance ofperfluorodimethylene-bis(perfluorovinyl ether) which is represented byCF₂ ═CF--O--CF₂ --CF₂ --O--CF═CF₂. In this polymerization method,however, there is a restriction such that the cyclic polymerization iscarried out only under a diluting condition where the monomerconcentration is 12% by weight or below. These patent specificationsmention that when the monomer concentration exceeds 12% by weight, thereis produced a polymer having a repeating unit of ##STR3## The fact thatthe monomer concentration should be kept at 12% or below isdisadvantageous in the industrial practice of the method.

According to the researches and studies made by the present inventor, incase the hydrocarbon-type monomers are used, the cyclic polymerizationcan be done relatively smoothly and advantageously without beinggoverned by the molecular structure of the monomeric substances.However, with regard to the fluorine-containing monomers having thefluorine content of 10% by weight or above, in particular perfluoromonomer, there has been scarcely known, to date, a method which iscapable of producing the polymer having the cyclic structure in its mainchain from a straight chain monomer in an industrially advantageous andsmooth manner, as has been described in the foregoing. In the case of afluorine-containing monomer having the above-mentioned symmetricalmolecular structure, the particular condition as mentioned above shouldnecessarily be adopted in the cyclic polymerization, and a point ofdifficulty is recognized generally in that gel is by-produced remarkablyto make it difficult to proceed the cyclic polymerization. Also, in thecyclic polymerization using the fluorine-containing monomer such as theabove-mentioned perfluoro-dimethylene-bis(perfluorovinyl ether), thereis recognized, in similar manner, the disadvantage of gel beingby-produced in the polymerization reaction, besides the restriction ofthe polymerization to be done under a high diluting condition asmentioned above, on account of the monomeric substance being symmetricalin its molecular structure.

The present inventor has been strenuously engaged in continuedresearches and studies on the method of producing thefluorine-containing polymer having the cyclic structure in its mainchain from a fluorine-containing monomer having the straight chain, asthe result of which he has come to a new observation and finding suchthat a fluorine-containing monomer with a fluorine content of 10% byweight or above is required to have a particular molecular structure forits advantageous cyclic polymerization. In more detail, the monomericsubstance should have in its molecules two polymerizing groups, eachhaving different polymerizability, and should have two to seven atoms inthe straight chain portion of a linking chain which links these twopolymerizing groups together. Thus, the present inventor has found outthat the fluorine-containing monomer having such particular molecularstructure, even in the case of perfluoro monomer, is, surprisinglyenough, capable of advancing the cyclic polymerization in a smooth andadvantageous manner by suppressing by-production of gel withoutnecessity whatsoever for adopting the very high pressure condition andthe high diluting condition.

The present invention has thus been completed on the basis of such newobservation and finding as mentioned above, and provides a novel cyclicpolymerization method, which is characterized in subjecting afluorine-containing monomer to the cyclic polymerization, thefluorine-containing monomer having two carbon-carbon multiple bonds,each having different polymerizability, as linked by a linking chainhaving a straight chain portion of from two to seven atoms, and having afluorine content of 10% by weight or above.

It is important in the present invention to use a fluorine-containingmonomer having a particular molecular structure. First of all, themonomer contains two carbon-carbon multiple bonds, each having differentpolymerizability. Usually, carbon-carbon double bond is adopted, or twomultiple bond having different kinds and structures is adopted. Examplesof such bond are: fluorine monomer having two multiple bonds ofasymmetrical structure; vinyl ether group and allyl group; vinyl ethergroup and vinyl group; fluorine-containing multiple bond and hydrocarbonmultiple bond; perfluoro multiple bond and partially fluorinatedmultiple bond; and so forth. In the second place, the number of atoms inthe straight chain portion of the linking chain for connecting these twocarbon-carbon multiple bonds is required to be from 2 to 7. In case thenumber of atoms in the straight chain portion of the linking chain iszero or 1, the cyclic polymerization is difficult to occur. The samething can be said when the number of atom is 8 or more. A preferrednumber of atoms should usually be from 2 to 5. Also, the linking chainis not limited to the straight chain form, but it may be in theside-chain structure or in the cyclic structure. Further, theconstituent atom is not limited to carbon, but various hetero-atoms suchas oxygen (O), sulfur (S), nitrogen (N), etc. may be contained therein.In the third place, the fluorine-containing monomer in the presentinvention has the fluorine content of 10% by weight or more. When thefluorine content is too low, it becomes difficult to exhibit thespecificity which the fluorine atom possesses. In the present invention,as a matter of course, perfluoro monomer is used preferably.

As the concentrate examples of the particular fluorine-containingmonomers as mentioned above, the following are enumerated. ##STR4##

For the purpose of the present invention, the fluorine-containingmonomer having a single vinyl ether group and being represented by CF₂═CFO-- is preferably adopted in points of its polymerization reactivity,cyclic polymerizability, suppression of gellation, and others.Particularly preferred examples are perfluoroallyl vinyl ether (CF₂═CFOCF₂ CF═CF₂) and perfluorobutenyl vinyl ether (CF₂ ═CFOCF₂ CF₂CF═CF₂).

These particular fluorine-containing monomers have been found to possessa surprising property such that it brings about the polymerization underrelatively moderate conditions to result in a polymer having the cyclicstructure in its main chain. The present invention has been reached onthe basis of this finding. That is to say, the polymerization method isnot at all restricted to any specific one, provided that thepolymerization proceeds radically. Examples are those polymerization, inwhich use is made of an inorganic radical initiator, light rays,ionizing radiation, or heat. As the radical initiator, there may beexemplified azo compounds such as 2,2'-azo-bis(N,N'-dimethyleneisobutylamine)dihydrochloride,2,2'-azo-bis(2-amidino-propane)dihydrochloride,2,2'-azo-bis(N,N'-dimethylene isobutyl amidine),4,4'-azo-bis(4-cyanopentanoic acid),2,2'-azo-bis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propioneamide}, 2,2'-azo-bis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]-propioneamide}, 2,2'-azo-bis[2-methyl-N-(2-hydroxyethyl)propione amide],2,2'-azo-bis(isobutyl amide)dihydrate,2,2'-azo-bis(4-methoxy-2,4-dimethyl valeronitrile),2,2'-azo-bis(2,4-dimethyl valeronitrile), (1-phenylethyl)azo-diphenylmethane, 2,2'-azo-bis-isobutyronitrile,dimethyl-2,2'-azo-bis-isobutyrate, 2,2'-azo-bis(2-methybutyronitrile),1,1'-azo-bis(1-cyclohexane carbonitrile), 2-(carbamoylazo)-isobutyronitrile, 2,2'-azo-bis(2,4,4-trimethyl pentane),2-phenylazo-2,4-dimethyl-4-methoxy valeronitrile, 2,2'-azo-bis(2-methylpropane); organic peroxides such as stearoyl peroxide, diisopropylperoxydicarbonate, benzoyl peroxyde, 2,4-dichlorobenzoyl peroxide,acetyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide,diisopropyl benzene hydroperoxide, para-methane-hydroperoxide,2,5-dimethyl hexane-2,5-dihydroperoxide, methylethyl ketone peroxide,cyclohexane peroxide, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxide)hexane,2,5-dimethyl-2,5-di(t-butyl peroxy)hexene-3, octanoyl peroxide, decanoylperoxide, lauroyl peroxide, t-butyl perbenzoate, t-butyl peracetate,t-butyl perpivalate, t-butyl perisobutylate, t-butyl peroxyisopropylcarbonate, di-t-butyl-di-perphthalate, t-butyl perlaurate,2,5-dimethyl-2,5-di(benzoyl peroxy)hexane, di-perfluorobutanoicperoxide, di-perfluoro-3-oxa-methylhexanoic peroxide, di-perfluorononaicperoxide and so forth; and inorganic peroxides such as K₂ S₂ O₈, (NH₄)₂S₂ O₈. Examples of the lights are visible light, ultra-violet rays,etc., with which photo-sensitizers may be used. As the ionizingradiation rays, there may be exemplified gamma rays, beta rays, alpharays from radioactive isotopes such as ⁶⁰ Co, ¹⁹² Ir, ¹⁷⁰ Tm, ¹³⁷ Cs andso on, and electron beams produced from an electron beam accelerator.

The polymerization method is also not particularly limitative, and theremay be used those various methods such as the so-calledbulk-polymerization, wherein monomeric substance is subjected to thepolymerization as it is; the solution-polymerization, wherein thepolymerization is conducted in fluoro-hydrocarbon, chloro-hydrocarbon,fluoro-chloro-hydrocarbon, alcohol, hydrocarbons, and other organicsolvents; the suspension-polymerization, wherein the polymerization iscarried out in an aqueous medium in the presence or absence of anappropriate organic solvent; the emulsion-polymerization, wherein thepolymerization is conducted in an aqueous medium with addition theretoof an emulsifier; and so fourth. No particular limitation is alsoimposed on the temperature and pressure for the polymerization. It is,however, desirable that they may be established appropriately by takinginto consideration various factors such as the boiling point of themonomer, the required heating source, the removal of heat frompolymerization, and so on. For instance, the temperature may beadequately set between 0° C. and 200° C., and an appropriate temperaturesetting can be done practically with a temperature ranging from a roomtemperature to 100° C. The pressure for the polymerization may either beunder a reduced pressure or be under an increased pressure. A suitablepolymerization can be carried out practically with a pressure rangingfrom a normal pressure to 100 atm, or so, and more preferably from anormal pressure to 50 atm, or so.

The cyclic polymerization method according to the present invention canbe applied to the homo-polymerization of one kind of the above-mentionedparticular fluorine-containing monomers, and can also be applied to thecopolymerization of two or more kinds of these fluorine-containingmonomers or the copolymerization of such monomer(s) with othermonomer(s). Such other monomers to be copolymerized with theabove-mentioned particular fluorine-containing monomers are not solimitative, provided that they have the radical-polymerizability, hencethey can be selected widely from fluorine-containing type, hydrocarbontype, and others. It goes without saying that only one kind of suchother monomers may be subjected to the radical copolymerization with theparticular fluorine-containing monomer, or two or more appropriate kindsof such other monomers may be subjected to the above-mentionedcopolymerization reaction. In order to make much use of thecharacteristics of the particular fluorine-containing monomer in thepresent invention, it is usually desirable that the fluorine-containingtype monomer such as fluoroolefin, fluorovinyl ether, etc. be selectedas such other monomer. Preferred examples are: tetrafluoroethylene,perfluoromethylvinylether, perfluoropropylvinylether,perfluorovinylethers having a functional group such as carboxyl group orsulfonic acid group, and so forth. There may also be used vinylidenefluoride, vinyl fluoride, chloro-tri-fluoro-ethylene, etc.

In the present invention, when the particular fluorine-containingmonomer is to be copolymerized with other monomer, there is noparticular reason to limit the ratio of copolymerization of theparticular fluorine-containing monomer. However, from the standpoint ofimproving various performances to be described later by introduction ofthe cyclic structure into the main chain, 0.1 mol % or more of theparticular fluorine-containing monomer in terms of the chargingcomposition is used with respect to such other monomer.

The fluorine-containing polymer to be obtained by the present inventioncontains therein the cyclic structure in its main chain, so that itpossesses high chemical stability and heat-resistance, in spite of itsbeing an amorphous, transparent polymer which is soluble in a solvent.In addition, it has a low refractive index, a high transmissibility tolight rays, and a high selective permeability to He, and so on. Further,the fluorine-containing polymer according to the present invention canbe formed into a vary thin film in a state of its being perfectly freefrom pin-hole and other defects, which has been difficult to achievewith the conventional fluorine-containing polymer. In view of suchcharacteristics properties, the field of application where thefluorine-containing polymer of the present invention exhibits itsusefulness are, for example, transparent coating material, paintingmaterial, insulating film, weather resistant film, optical material,separating membrane, and others.

In the present invention, when the particular fluorine-containingmonomer is copolymerized with other monomer, for example, with CF₂ ═CF₂,the crystallinity of such copolymer can be made lower than that ofpolytetrafluoroethylene (hereinafter abbreviated as "PTFE"). As theconsequence of this, the copolymer becomes feasible for themelt-forming, and its transparency is also improved. Moreover, when thecomposition of the cyclic portion of this copolymer is increased, itbecomes meltable and can be formed into film by casting. That is to say,the resulting copolymer with tetrafluoroethylene becomes easier thanPTFE in its shaping, on account of which the copolymer can be used forvarious shaped bodies having the performance of the fluorine-containingresin, which is equal to that of PTFE. Further, the copolymer can beused for various coating material, electronics parts, optical materials,etc., taking advantage of its transparency and cast-film forming.

When the fluorine-containing monomer is copolymerized with CF₂ ═CH₂, thetransparency of the resulted copolymer improves in comparison withhomopolymer of vinylidene fluoride (hereinafter abbreviated as "PVdF"),owing to lowering in its crystallinity and reduction in its crystalgrain size. Its refractive index can also be lowered, and its fluorinecontent can be increased without decreasing its high mechanical strengthwhich is one of the characteristic properties of PVdF. Accordingly, thiscopolymer is applicable to the entire fields where PVdF is being usedcurrently. In particular, it is most suitable for the fishing stringowing to its lowered refractive index and improved transparency. It canalso be used for electronics parts and optical parts as the transparentdielectric material. Furthermore, since the copolymer can be formed intofilm by casting and has high fluorine content, it can be used forproviding various shaped bodies and various coating materials, all ofwhich are more excellent than PVdF in its weather-resistant property,solvent-resistant property, heat-resistant property, and chemicalstability.

As mentioned above, when any of those known fluorine-containing typemonomer and the particular fluorine-containing monomer according to thepresent invention are copolymerized, the crystallinity of the resultedcopolymer can be lowered, or its crystal grain size can be reduced withthe consequence that its transparency improves and its melt-formingbecomes possible. Also, its mechanical strength such as elasticity, etc.becomes increased. Further, when the composition of the particularfluorine-containing monomer is increased, the obtained copolymer becomessoluble in solvent with the consequent improvement in its opaqueness,shapability, mechanical strength, etc. which are the disadvantageouslyvulnerable properties of the conventional fluorine-containing polymer.

When the hydrocarbon type monomer is subjected to copolymerization withthe particular fluorine-containing monomer, the resultant copolymerbecomes capable of retaining the characteristic feature of thefluorine-containing polymer without lowering the performance as thehydrocarbon type polymer, as compared with those hydrocarbon typecopolymers and those fluorine-containing type copolymers such as PTFE,PVdF, etc. While the reason for this is still to be clarified, it isconsidered that the fluorine portion in these copolymers exhibits thecyclic structure and does not produce crystals.

In other aspects, the fluorine-containing polymer to be obtained by thepresent invention has high gas-separating capability on account itsbeing able to introduce thereinto the fluorine-containing cyclicstructure, hence it can also be used as the material for gas-separatingmembrane.

In the present invention, the mechanism of the cyclic polymerization,wherein adoption of the very high pressure condition and high dilutingcondition is no longer required owing to use of the particularfluorine-containing monomer, is yet to be clarified. However, onethought may be given in that the connecting chain with an appropriatelength, in particular, the C--O--C bond, has sufficient flexibility,which makes it easy for the two multiple bonds to come closer eachother, whereby the cyclic polymerization proceeds even under a lowpressure. It may further be considered that, since the two multiplebonds which have been bonded together through the above-mentionedconnecting chain possess different polymerization reactivity, there isan increase in the mutual polymerizability with the consequence that theby-production of gel during the polymerization reaction can besuppressed without adoption of the high diluting condition.Incidentally, the preceding explanations are only for assisting the goodunderstanding of the present invention, hence it goes without sayingthat they are not intent on limiting the scope of the present invention.

In the following, the present invention will be explained in furtherdetails in reference to preferred and actual examples thereof. It shouldalso be understood that these examples are only illustrative of thepresent invention and do not intent to limit the scope of the presentinvention.

EXAMPLE 1

30 g of perfluoroallyl vinyl ether (hereinafter abbreviated as "PAVE")and 0.3 g of diisopropyl peroxy dicarbonate (hereinafter abbreviated as"IPP") were placed in a glass flask of a 100 cc capacity. Afterrepetition of the degassing under freezing condition for two times, thepolymerization was conducted for 16 hours at 25° C. The pressure duringthe polymerization was lower than the atmospheric pressure. After thepolymerization reaction, there was obtained 4.5 g of a polymer.

Upon measurement of the infrared ray absorption spectrum of thispolymer, there could be observed no absorption in the vicinity of 1790cm⁻¹ to be derived from the double bond which was present in thestarting monomeric substance. Further, when this polymer was dissolvedin perfluorobenzene and its ¹⁹ F NMR spectrum was measured, there wasobtained the spectrum which indicated the following repeating structure.##STR5## The intrinsic viscosity of this polymer [η] was 0.50 at 30° C.in a liquid which is composed principally of "FLUORINATE FC-75"(tradename for perfluoro(2-butyltetrahydrofuran) of 3M Corp, U.S.A.,which will hereinafter be abbreviated as "FC-75"). This indicates thatthe polymer has high degree of polymerization.

The glass transition point of this polymer was 69° C. At a roomtemperature, this polymer assumed a state of tough and transparentglass. Further, its 10% thermal decomposition temperature was 462° C.,which indicated that the polymer had high thermal stability.Furthermore, this polymer had colorless transparency, a low refractiveindex of 1.34, and a high light transmission factor of 95%.

The gas permeability coefficient of this polymer to various gases wasmeasured, the result of the measurement and the ratio of the permeationcoefficient being shown in the following Table.

    ______________________________________                                               Permeation                                                                    Coefficient                                                                   × 10.sup.10       Ratio                                                 (cm.sup.3 cm/cm.sup.2                                                                       Pair of   Permeation                                     Gas    sec cm11 g)   Gases     Coefficient                                    ______________________________________                                        He     106           He/N.sub.2                                                                              122                                            H.sub.2                                                                              26            He/CH.sub.4                                                                             452                                            CO.sub.2                                                                             8.6           CO.sub.2 /CH.sub.4                                                                      35                                             O.sub.2                                                                              3.9           H.sub.2 /CO                                                                             --                                             Ar     --            H.sub.2 /N.sub.2                                                                        30                                             N.sub.2                                                                               0.87         O.sub.2 /N.sub.2                                                                        4.4                                            CO     --                                                                     CH.sub.4                                                                              0.24                                                                  ______________________________________                                    

EXAMPLE 2

10 g of PAVE, 10 g of trichlorotrifluoroethane (hereinafter abbreviatedas "R-113"), and 10 mg of polymerization initiator (IPP) were placed ina glass flask of a 50 cc capacity. After repetition of the degassingunder freezing condition for two times, the polymerization was conductedfor 14 hours at 40° C. The pressure during the polymerization was lowerthan the atmospheric pressure. After the polymerization reaction, therewas obtained 6.1 g of a polymer.

The intrinsic viscosity of this polymer [η] was 0.37 at 30° C. in"FC-75", hence the resulted polymer was found to have a high molecularweight. It was also discovered from the ¹⁹ F NMR spectrum measurementthat the polymer was similar to that as obtained in Example 1 above.

EXAMPLE 3

30 g of PAVE and 10 mg of the polymerization initiator ##STR6## wereplaced in a glass flask of a 50 cc capacity. After repetition of thedegassing under freezing condition for two times, the polymerization wasconducted for 16 hours at 30° C. The pressure during the polymerizationwas lower than the atmospheric pressure. After the polymerizationreaction, there was obtained 16 g of a polymer.

The intrinsic viscosity of this polymer [η] was 0.505 at 30° C. in"FC-75".

EXAMPLE OF SYNTHESIS 1 Synthesis of CF₂ ═CFOCF₂ CF₂ CH═CH₂

Through the reaction of CF₂ ═CFOCF₂ CF₂ Br and chlorine gas, there wassynthesized a chlorine-added substance (CF₂ ClCFClOCF₂ CF₂ Br), thevinyl group of which had been protected. Subsequently, thischlorine-added substance and ethylene were reacted in an auto-clave inthe presence of a radical initiator, thereby synthesizing anehtylene-added substance (CF₂ ClCFClOCF₂ CF₂ CH₂ CH₂ Br), to which 1 molof ethylene was added.

Subsequently, the ethylene-added substance was treated with a mixedsolution of KOH and ethanol to thereby carry out removal of HBr,followed by further removal of Cl₂ with a mixture of Zn and dioxane. Asthe result, there was obtained the intended substance of CF₂ ═CFOCF₂ CF₂CH═CH₂ having a boiling point of 72° to 73° C. The structure of thefluorine-containing monomer was determined by measurement of ¹⁹ F NMRand ¹ H NMR. spectra.

EXAMPLE 4

40 g of CF₂ ═CFOCF₂ CF₂ CH═CH₂ as obtained in the above Example ofSynthesis 1 and 20 g of "R-113" were charged in a three-necked flaskwhich had been substituted with nitrogen. To this charge in the flask,there was added ##STR7## as the polymerization initiator in a quantityof 10 mg, and the reaction system was further substituted with nitrogen,after which the polymerization was conducted for five hours at 18° C. Asthe result, there was obtained 30 g of a polymer. This polymer could bedissolved in "R-113" and had an intrinsic viscosity [η] of 0.96 at 30°C. in metaxylenehexafluoride. It was also verified from the ¹⁹ F NMR and¹ H NMR spectra measurements that the polymer was a cyclic polymerhaving the following repeating structure. ##STR8##

EXAMPLE 5

5 g of PAVE, 15 g of "R-113", and 80 mg of 5 wt % solution of thepolymerization initiator ##STR9## were charged in an ampoule of a 100 mlcapacity and made of pressure-resistant glass. After repetition ofdegassing under freezing condition for three times, 0.5 g of CF₂ ═CF₂was charged in the reaction system. While shaking the ampoule in anincubator, the polymerization was conducted for six hours at 30° C.,from which a solid substance was obtained in a quantity of 1.5 g.

The thus obtained solid substance was dissolved in perfluoro-benzene,and its structure was verified by the ¹⁹ F NMR spectrum measurement. Asthe result, it was found out that the polymer as obtained was acopolymer of a cyclic structure unit as shown below and atetrafluoroethylene unit, wherein a mol ratio between a and b (a/b) was1/0.52. ##STR10## It was also found out that this copolymer had itsintrinsic viscosity [η] of 0.425 at 30° C. in "FC-75".

EXAMPLE 6

5 g of PAVE, 15 g of "R-113" and 50 mg of 5 wt % "R-113" solution of thepolymerization initiator ##STR11## were charged in an ampoule having a100 ml capacity and made of pressure-resistant glass. After repetitionof degassing under freezing condition for three times, 0.5 g of CF₂ ═CF₂was charged into the reaction system. Then, the polymerization wasconducted for 45 minutes at 30° C., from which a white powder wasobtained in a quantity of 1.8 g. The thus obtained solid substance wasfound to be a copolymer similar to that obtained in Example 5 above asthe result of the ¹⁹ F NMR spectrum measurement.

EXAMPLE 7

5 g of PAVE, 25 g of pure water, 0.09 g of C₈ F₁₇ CO₂ NH₄, 0.073 g ofNaH₂ PO₄, and 0.0132 g of ammonium persulfate were charged in an ampouleof a 100 ml capacity and made of pressure-resistant glass. After thereaction system was sufficiently substituted with nitrogen gas, 0.5 g ofCF₂ ═CF₂ was charged into the system and the polymerization reaction wasconducted for 16 hours at 60° C., while shaking the ampoule in anincubator, as the result of which there was produced 2.5 g of a solidsubstance.

The thus obtained solid substance was dissolved in perfluoro-benzene,and its structure was verified by means of the ¹⁹ F NMR spectrummeasurement. Further, this copolymer had its intrinsic viscosity [η] of0.30 at 30° C. in "FC-75".

EXAMPLE 8

20 g of PAVE, 60 g of "R-113", and 20 mg of diisopropylperoxydicarbonate as the polymerization initiator were placed in anampoule having a 200 ml capacity and made of pressure-resistant glass.In the same manner as in Example 5 above, CH₂ ═CF₂ was charged into thereaction system and the polymerization was conducted for 4.5 hours underthe same conditions as in Example 5, from which 12.3 g of a solidsubstance soluble in acetone was obtained.

EXAMPLE 9

5 g of PAVE, 8.74 g of perfluoropropyl-perfluorovinylether, and 5 g of2,2'-azo-bis-isobutyronitrile were placed in an ampoule having a 100 mlcapacity and made of pressure-resistant glass. After repeating thedegassing under freezing condition for three time, the polymerizationwas conducted for 16 hours at 60° C., while shaking the ampoule in anincubator. After completion of the reaction, there was obtained 0.9 g ofa solid substance.

EXAMPLE OF SYNTHESIS 2

Synthesis of CF₂ ═CFCF₂ CF₂ CH═CH₂ 250 g of CF₂ ClCFClCF₂ CF₂ CH₂ CH₂ I(as synthesized in accordance with the method as described in JapaneseUnexamined Patent Publication No. 64940/1985) was treated with a mixedsolution of KOH and methanol to thereby remove hydrogen and iodine,followed by further removal of chlorine with a mixture of Zn anddioxane, whereby 100 g of CF₂ ═CFCF₂ CF₂ CH═CH₂ having a boiling pointof 66° C. was obtained. The structure of this fluorine-containingmonomer was verified by the ¹⁹ F NMR and ¹ H NMR spectra measurements.

EXAMPLE OF SYNTHESIS 3

Synthesis of CH₂ ═CH(CF₂)₄ CH═CH₂ By a known method, CH₂ ═CH(CF₂)₄CH═CH₂ was synthesized from α,ω-diiodoperfluorobutane in two-stagereaction (ethylene addition reaction and hydrogen and iodine removingreaction).

EXAMPLE 10

21 g of CF₂ ═CFCF₂ CF₂ CH═CH₂ as obtained in the above-described Exampleof Synthesis 2 and 38 g of "R-113" were placed in a three-necked flask,to which 15 mg of ##STR12## as the polymerization initiator was added.After the reaction system was further substituted with nitrogen, thepolymerization reaction was conducted for 12 hours at 20° C. As theresult, there was obtained 14 g of a polymer. This polymer could bedissolved in tetrahydrofuran (hereinafter abbreviated as "THF"), and hadits intrinsic viscosity [η] of 0.62 at 30° C. in THF.

COMPARATIVE EXAMPLE

The same procedure as in Example 10 above was followed, with theexception that 25.4 g of CH₂ ═CH(CF₂)₄ CH═CH₂ obtained in the aboveExample of Synthesis 3 was used in place of CF₂ ═CFCF₂ CF₂ CH═CH₂,thereby carrying out the polymerization. No polymer having highmolecular weight could be obtained after 12 hours' polymerizationreaction.

EXAMPLE OF SYNTHESIS 4

Synthesis of CF₂ ═CFOCF₂ CF₂ CF═CF₂ 2,000 g of CF₂ ClCFClCF₂ COF wasreacted with hexafluoro-propyleneoxide in the presence of cesiumfluoride, and was further converted into potassium salt thereof by useof potassium hydroxide, after which the substance was subjected tothermal decomposition, thereby obtaining CF₂ ClCFClCF₂ CF₂ OCF═CF₂ asthe product. Subsequently, this product was reacted with a mixture of Znand dioxane to carry out removal of chlorine, thereby obtaining 300 g ofCF₂ ═CFCF₂ CF₂ OCF═CF₂ having a boiling point of 64° C. The structure ofthis fluorine-containing monomer was verified by the ¹⁹ F NMR spectrummeasurement.

EXAMPLE 11

5.42 g of CF₂ ═CFOCF₂ CF₂ CF═CF₂ (hereinafter abbreviated as "PBVE" asobtained in the above-described Example of Synthesis 4 and 10 mg of thepolymerization initiator ##STR13## were placed in an ampoule having aninner volume of 50 ml and made of pressure-resistant glass. Afterdegassing under freezing condition was repeated for two times, thepolymerization reaction was conducted for 48 hours at 25° C. Thepressure during the polymerization reaction was lower than theatmospheric pressure. From this polymerization reaction, there wasobtained 2.22 g of a polymer.

When the infrared ray absorption spectrum of this polymer was measured,there could be observed no absorption in the vicinity of 1790 cm⁻¹ to bederived from the double bond which was present in the starting monomericsubstance. Further, when this polymer was dissolved in perfluorobenzeneand its ¹⁹ F NMR spectrum was measured, there was obtained the spectrumwhich indicated the following repeating structure. ##STR14## Theintrinsic viscosity of this polymer [η] was 0.55 at 30° C. in "FC-75",which indicated that this polymer had a high degree of polymerization.

The glass transition temperature of this polymer was 108° C. At a roomtemperature, this polymer assumed a state of tough and transparentglass. Also, it had 10% thermal decomposition temperature of 457° C.,thus indicating high thermal stability. By the way, this polymer wascolorless transparent, and had its refractive index of as low as 1.34and its light transmission factor of as high as 95%.

EXAMPLE 12

5 g of PAVE, 5 g of PBVE and 10 mg of the polymerization initiator##STR15## were placed in a glass reactor having an inner volume of 60ml. After the degassing under freezing condition for two times,polymerization was conducted for 24 hours at 25° C., while agitating thereactants. The pressure during the polymerization reaction as lower thanthe atmospheric pressure. As the result, there was obtained 5.5 g of apolymer.

When the infrared ray absorption spectrum of this polymer was measured,there could be observed no absorption in the vicinity of 1790 cm⁻¹ to bederived from the double bond which was present in the starting monomericsubstance. Further, this polymer was dissolved in perfluorobenzene andits ¹⁹ F-NMR spectrum was measured to verify its structure. As theresult, the obtained polymer was found to be a copolymer consisting of:a unit of the cyclic structure to be derived from PAVE such asrepresented by the following formula: ##STR16## and a unit of the cyclicstructure to be derived from PBVE such as represented by the followingformula: ##STR17## and containing therein 54% by weight of the unit ofthe cyclic structure to be derived from PAVE.

This polymer was found to have its intrinsic viscosity [η] of 0.44 at30° C. in "FC-75", hence high degree of polymerization.

The glass transition point of this polymer was 91° C. and indicated astate of its being tough and transparent glass at a room temperature.Further, its 10% thermal decomposition temperature was 435° C., thusindicating that the polymer had high thermal stability. Furthermore,this polymer was colorless transparent, and had its refractive index ofas low as 1.34 and its light transmission factor of as high as 95%.

EXAMPLE 13

20 g of PBVE obtained in Example of Synthesis 4 and 40 mg of thepolymerization initiator ##STR18## were placed in an ampoule having aninner volume of 200 ml and made of pressure-resistant glass. Afterrepetition of the degassing under freezing condition for two times, 1.0g of CF₂ ═CFCl was charged into the reaction system. While shaking theampoule in an incubator, the polymerization reaction was conducted for10 hours at 25° C. As the result, there was obtained a polymer in aquantity of 4.5 g.

Upon measurement of the infrared ray absorption spectrum of thispolymer, it was found that there was no absorption in the vicinity of1790 cm⁻¹ due to the double bond which was present in the startingmonomeric substance. Further, this polymer was dissolved intoperfluorobenzene, and its structure was verified by measurement of the¹⁹ F-NMR spectrum. As the result, the thus obtained polymer was found tobe a copolymer consisting of: a unit of the cyclic structure to bederived from PBVE such as represented by the following formula:##STR19## and a unit of the structure to be derived from CF₂ ═CFCl asrepresented by the following formula: ##STR20## and containing therein84% by weight of the unit of the cyclic structure to be derived fromPBVE. This polymer had its intrinsic viscosity of 0.43 in "FC-75" at 30°C., thus indicating that it had high degree of polymerization.

The polymer was in a state of its being tough and transparent glass at aroom temperature. It had also a 10% thermal decomposition temperature of421° C., which showed that it had high thermal stability. Further, thepolymer showed its solubility in a mixed solution of "FC-75" and"R-113".

EXAMPLE 14

20 g of PBVE obtained in Example of Synthesis 4 above and 20 mg of thepolymerization initiator ##STR21## were placed in an ampoule having aninner volume of 200 ml and made of pressure-resistant glass. Afterrepetition of the degassing under freezing condition for two times, 0.5g of CF₂ ═CF₂ was charged in the reaction system. While shaking thisampoule in an incubator, the polymerization reaction was conducted forfive hours at a temperature of 25° C. As the result, there was obtained5.8 g of a polymer.

Upon measurement of the infrared ray absorption spectrum of thispolymer, there could be observed no absorption in the vicinity of 1790cm⁻¹ to be derived from the double bond which was present in thestarting monomeric substance. Further, this polymer was dissolved inperfluorobenzene to measure its ¹⁹ F-NMR spectrum, from which itsstructure was verified. As the result of this, the thus obtained polymerwas found to be a copolymer consisting of: a unit of the cyclicstructure to be derived from PBVE such as represented by the followingformula: ##STR22## and a unit of the structure to be derived from CF₂═CF₂ as represented by the following formula: ##STR23## and containingtherein 94% by weight of the unit of the cyclic structure to be derivedfrom PBVE. Further, this polymer had its intrinsic viscosity [η] of 0.53in "FC-75" at 30° C., thus indicating that it had high degree ofpolymerization. It also indicated a state of its being a tough andtransparent polymer at a room temperature.

EXAMPLE 15

9 g of PAVE, 1 g of CF₂ ═CF--O--CF₂ CF₂ CF₂ COOCH₃, and 10 mg of thepolymerization initiator ##STR24## were placed in an ampoule having aninner volume of 50 ml and made of pressure-resistant glass. Afterrepetition of the degassing under freezing condition for two times, thepolymerization was conducted for 24 hours at a temperature of 25° C. Thepressure during the polymerization reaction was lower than theatmospheric pressure As the result, there was obtained 3.55 g of apolymer.

This polymer was dissolved in perfluorobenzene to measure its ¹⁹ F-NMRspectrum, from which its structure was verified. As the result, the thusobtained polymer was found to be a copolymer consisting of a unit of thecyclic structure to be derived from PAVE such as represented by thefollowing formula: ##STR25## a unit of the structure of the formula:##STR26## and containing therein 93% by weight of the unit of the cyclicstructure to be derived from PAVE.

This polymer had its intrinsic viscosity [η] of 0.32 in "FC-75" at 30°C., thus indicating that it had a high degree of polymerization.

The polymer had its glass transition point of 64° C., and indicated astate of its being tough and transparent glass. Also, its 10% thermaldecomposition temperature was 430° C., thus indicating that it had highthermal stability. Further, this polymer was colorless transparent.

EXAMPLE 16

40 g of PAVE, 5 g of CF₂ ═CF--O--CF₂ CF₂ CF₂ COOCH₃, and 10 mg ofdiisopropyl peroxydicarbonate as the polymerization initiator wereplaced in an ampoule having an inner volume of 100 ml and made ofpressure-resistant glass. After repetition of the degassing underfreezing condition for two times, 5 g of CF₂ ═CF₂ was charged into thereaction system. While shaking this ampoule in an incubator, thepolymerization was conducted for 72 hours at a temperature of 30° C. Asthe result, there was obtained 11.8 g of a polymer.

This polymer was dissolved in perflurobenzene to measure its ¹⁹ F-NMRspectrum, from which its structure was verified. As the result, the thusobtained polymer was found to be a copolymer consisting of: a unit ofthe cyclic structure to be derived from PAVE such as represented by thefollowing formula: ##STR27## and units of the formulas: ##STR28##derived from CF₂ ═CF--O--CF₂ CF₂ CF₂ COOCH₃ and CF₂ ═CF₂, respectively,and containing therein 82% by weight of the unit of the cyclic structureto be derived from PAVE.

This polymer had its intrinsic viscosity [η] of 0.42 in "FC-75" at 30°C., thus indicating that it had high degree of polymerization.

The polymer was found to have its glass transition point of 58° C., andindicated a state of its being tough and transparent polymer at a roomtemperature. Further, its 10% thermal decomposition temperature was 421°C., thus indicating that it had high thermal stability. Furthermore, thepolymer was colorless transparent.

EXAMPLE 17

8 g of PBVE, 1 g of CF₂ ═CFOCF₂ CF(CF₃)OCF₂ CF₂ SO₂ F and 10 mg of thepolymerization initiator ##STR29## were placed in an ampoule having aninner volume of 50 ml and made of pressure-resistant glass. Afterrepetition of the degassing under freezing condition for two times,polymerization was conducted for 24 hours at 25° C. The pressure duringthe polymerization reaction was lower than the atmospheric pressure. Asthe consequence, there was obtained 3.8 g of a polymer. This polymer wasdissolved in perfluorobenzene to measure its ¹⁹ F-NMR spectrum, fromwhich its structure was verified. As the result, the thus obtainedpolymer was found to be a copolymer consisting of: a unit of the cyclicstructure to be derived from PBVE such as represented by the followingformula: ##STR30## and a unit of the structure to be derived from CF₂═CFOCF₂ CF(CF₃)OCF₂ CF₂ SO₂ F as represented by the following formula:##STR31## and containing therein 94% by weight of the unit of thestructure to be derived from PBVE.

It was found that this polymer had its intrinsic viscosity [η] of 0.38in "FC-75" at 30° C., thus indicating that it had high degree ofpolymerization.

The polymer had its glass transition point of 92° C., and indicated astate of its being tough and transparent glass. The polymer wascolorless transparent. The adhesive property of this polymer with glasswas satisfactory.

EXAMPLE 18

8 g of PAVE, 2 g of CF₂ ═CF--O--CF₂ CF₂ CF₃, and 10 mg of thepolymerization initiator ##STR32## were placed in an ampoule having aninner volume of 50 ml and made of pressure-resistant glass. Afterrepetition of the degassing under freezing condition for two times, thepolymerization was conducted for 24 hours at a temperature of 25° C. Thepressure during the polymerization reaction was lower than theatmospheric pressure. As the result, there was obtained a polymer in aquantity of 1.85 g.

This polymer was dissolved in perfluorobenzene to measure its ¹⁹ F-NMRspectrum, from which its structure was verified. As the consequence, thethus obtained polymer was found to be a copolymer consisting of: a unitof the cyclic structure to be derived from PAVE such as represented bythe following formula: ##STR33## a unit of the structure to be derivedfrom CF₂ ═CF--O--CF₂ CF₂ CF₃ as represented by the following formula:##STR34## and containing therein 89% by weight of the unit of the cyclicstructure to be derived from PAVE.

It was further found that this polymer had its intrinsic viscosity [η]of 0.35 in "FC-75" at 30° C., thus indicating that it had high degree ofpolymerization.

The polymer had its glass transition point of 61° C., and indicated astate of its being tough and transparent glass. Furthermore, its 10%thermal decomposition temperature was 415° C., thus indicating that thepolymer had high thermal stability. Moreover, this polymer was colorlesstransparent, and showed its elongation of 250% at 25° C.

The present invention has its excellent effect such that, by adoption ofthe particular fluorine-containing monomers as the component for thepolymerization, it is able to produce advantageously and smoothly thefluorine-containing polymer having the cyclic structure in the mainchain of the polymer. In particular, it has such effect that achievesthe cyclic polymerization of the straight chain monomer without adoptingthe very high pressure condition and the high diluting condition. It canfurther be recognized that, by adoption of those monomers havingparticular molecular structure, by-production of the gel during thepolymerization reaction can be effectively suppressed.

Furthermore, the present invention has such an effect that, on accountof its being able to introduce into the main chain of various polymersthe cyclic structure, particularly the fluorine-containing cyclicstructure, various excellent and useful properties can be imparted tothe resulting fluorine-containing polymers. That is to say, thefluorine-containing polymer having the cyclic structure in the mainchain, to be obtained by the present invention, is such one that isamorphous, transparent and soluble in solvent, while retaining itsexcellent properties of the fluorine-containing polymer such as, forexample, heat-resistance, chemical stability, and so forth. From suchcharacteristic features, the fluorine-containing polymer of the presentinvention is recognized to have such effect that it can be formed intoan ultra-thin film free from defects such as pin-hole, etc., hence itfinds wide varieties of use as the optical material, the coatingmaterial, the material for separating membrane, and others. To add more,when it is used in combination with, for example, PTFE and otherconventional fluorine-containing polymers, the fluorine-containingpolymer of the present invention is able to give its useful propertiesof non-crystallinity, transparency, solubility to solvent, and so on,without impairing the desirable properties inherent in thefluorine-containing polymer such as heat-resistance, chemical stability,electrical characteristic, etc. Such combined use of thefluorine-containing polymer of the present invention and thoseconventional fluorine-containing polymer still makes it possible to forman ultra-thin film.

We claim:
 1. A method for cyclic polymerization, which comprisessubjecting a fluorine-containing monomer to cyclic polymerization, saidfluorine-containing monomer having two acyclic carbons bonded to eachother by a multiple bond, one carbon of which is linked by a linkingchain to one carbon of two other acyclic carbons bonded to each other bya multiple bond, the carbon-carbon multiple bonds each having differentpolymerizability, the linking chain having a straight chain portion offrom 2 to 7 atoms, and the monomer having a fluorine content of at least10% by weight, said cyclic polymerization being carried out with aninitial monomer concentration of said monomer of greater than 12% byweight.
 2. A method according to claim 1, wherein saidfluorine-containing monomer contains therein the multiple bonds selectedfrom: two multiple bonds of asymmetrical structure, a vinyl ether groupand an allyl group, a vinyl ether group and a vinyl group, afluorine-containing multiple bond and a hydrocarbon multiple bond, or aperfluoro multiple bond and a partially fluorinated multiple bond.
 3. Amethod according to claim 1, wherein said fluorine-containing monomer iscopolymerized with another fluorine-containing monomer or a hydrocarbonmonomer.
 4. A method according to claim 1, wherein said cyclicpolymerization is carried out by bulk polymerization,solution-polymerization, suspension-polymerization, oremulsion-polymerization.
 5. A method according to claim 1, wherein saidcyclic polymerization is carried out at a temperature ranging from zeroto 200° C., and under a reduced pressure or a pressure ranging fromnormal pressure to 100 atm.
 6. A method according to claim 1, whereinsaid fluorine-containing monomer is homo-polymerized or co-polymerized.7. A method according to claim 1, wherein said fluorine-containingmonomer is copolymerized with other monomer or fluorine-containing typeor hydrocarbon type.
 8. The method of claim 1 wherein one of themultiple bonds is in the structure CF₂ ═CF-- and the other is in thestructure CF₂ ═CF-- or CH₂ ═CH--.
 9. The method of claim 1 wherein thefluorine-containing monomer is CF₂ ═CFOCF₂ CF═CF₂, CF₂ ═CFOCF₂ CF₂CF═CF₂, CF₂ ═CFOCF₂ CF═CH₂, ##STR35##
 10. The method of claim 8 whereinthe fluorine containing monomer is perfluoroallyl vinyl ether.
 11. Themethod of claim 8 wherein the fluorine containing monomer is CF₂ ═CFOCF₂CF═CF₂.
 12. The method of claim 8 wherein said fluorine-containingmonomer is copolymerized with tetrafluorothylene or vinylidene fluoride.